Very impressed with your bungee cord and duct tape approach to brewing low tech is the way forward. I've made a bucket in bucket mash tun which works great. However the insulation is annoying to clean and remove to turn the tun into a fermenter so I'm planning on using the Lidl cooler with a muslin filter.
I've found it difficult to locate a big sheet of muslin and found just sheets of Nylon. Where are you getting the muslin?
also is there a good mash efficiency using the muslin?
It cost around £4 in total including postage for 2 square metres of it. I haven't used it just yet, but it seems grand. I would have bought more of it, but wanted to check out the quality of it first. I'll hopefully use it on Sunday, so hang on til then if you want me to report back on it before buying online.